The present invention relates to a semiconductor light-emitting device such as light-emitting diodes to be used for display, optical communications and the like, and also to a manufacturing method therefor. The invention further relates to an LED lamp and an LED display, whichever is equipped with such a semiconductor light-emitting device.
In recent years, there have been developed high-intensity light-emitting diodes (LEDs) which emit light of infrared to blue wavelengths. This is based on the fact that the crystal growth technique for direct-transition group III-V compound semiconductor materials has been improved dramatically so that crystal growth has become implementable for almost any semiconductor that belongs to the group III-V compound semiconductors. LEDs using these direct-transition materials, by virtue of their capability of high-output, high-intensity emission, have come to be widely used as high-intensity LED lamps such as outdoor display boards, display-use light sources such as indicator lamps for portable equipment of low power consumption, and light sources for optical transmission and optical communications by plastic optical fibers.
As a new high-output, high-intensity LED of this type, there has been known an LED using AlGaInP-based material as shown in FIG. 11. This LED is fabricated by the following process. That is,
On an n-type GaAs substrate 1, are stacked one after another:
an n-type GaAs buffer layer 2;
a distributed Bragg reflector layer (dopant concentration: 5xc3x971017 cmxe2x88x923) 4 made of a multilayer film in which n-type (AlxGa1xe2x88x92x)0.51In0.49P (x=0.45) and n-type Al0.51In0.49P are stacked alternately;
an n-type (AlxGa1xe2x88x92x)0.51In0.49P lower cladding layer (0xe2x89xa6xxe2x89xa61, e.g. x=1.0; thickness: 1.0 xcexcm; dopant concentration: 5xc3x971017 cmxe2x88x923) 5;
a p-type (AlxGa1xe2x88x92x)0.51In0.49P active layer (0xe2x89xa6xxe2x89xa61, e.g. x=0.42; thickness: 0.6 xcexcm; dopant concentration: 1xc3x971017 cmxe2x88x923) 6; and
a p-type (AlxGa1xe2x88x92x)0.5In0.49P upper cladding layer (0xe2x89xa6xxe2x89xa61, e.g. x=1.0; thickness: 1.0 xcexcm; dopant concentration: 5xc3x971017 cmxe2x88x923) 7,
and further thereon are formed:
a p-type (AlxGa1xe2x88x92x)vIn1xe2x88x92vP intermediate layer (x=0.2; v=0.4; thickness: 0.15 xcexcm; dopant concentration: 1xc3x971018 cmxe2x88x923) 8;
a p-type (AlxGa1xe2x88x92x)vIn1xe2x88x92vP current spreading layer (x=0.05; v=0.05; thickness: 1.5 xcexcm; dopant concentration: 5xc3x971018 cmxe2x88x923) 10; and
an n-type GaP current blocking layer (thickness: 0.3 xcexcm; dopant concentration: 1xc3x971018 cmxe2x88x923) 9.
Thereafter, the n-type GaP current blocking layer 9 is subjected to selective etching by normal photolithography process so that a 50 xcexcm to 150 xcexcm-dia. portion thereof shown in the figure is left while its surrounding portions are removed. A p-type (AlxGa1xe2x88x92x)vIn1xe2x88x92vP current spreading layer (x=0.05; v=0.95; thickness: 7 xcexcm; dopant concentration 5xc3x971018 cmxe2x88x923) 10 is regrown in such a manner as to cover the top of the p-type (AlxGa1xe2x88x92x)vIn1xe2x88x92vP current spreading layer, which has been exposed by removing the n-type GaP current blocking layer 9, as well as the n-type GaP current blocking layer 9.
Finally, on the p-type current spreading layer 10 is deposited, for example, a Auxe2x80x94Be film. This film is patterned into a circular form, for example, so as to be inverse to the light-emitting region, thereby forming a p-type electrode 12. Meanwhile, on the lower surface of the GaAs substrate 1 is formed, for example, an n-type electrode 11 made of a Auxe2x80x94Zn film by deposition.
It is noted here that, for simplicity"" sake, the ratio x of Al to Ga, the ratio v of totaled Al and Ga to the other group III elements, or the like will be omitted as appropriate in the following description.
With respect to the p-type AlGaInP current spreading layer 10, the Al composition xe2x80x9cxxe2x80x9d and the In composition (1xe2x88x92v) are set low, as already described, so that the current spreading layer becomes transparent to the emission wavelength range 550 nm-670 nm of this AlGaInP-based LED, low in resistivity, and makes ohmic contact with the p-side electrode (i.e., x=0.05, v=0.95). In the AlGaInP-based LED, normally, Si is used as the n-type dopant, and Zn is used as the p-type dopant. Also, the conductive type of the active layer is normally the p type.
As the substrate for (AlxGa1xe2x88x92x)vIn1xe2x88x92vP-based LEDs, normally, a GaAs substrate is used so as to obtain lattice matching with materials of individual layers. However, the GaAs substrate has a band gap of 1.42 eV, lower than those of (AlxGa1xe2x88x92x)vIn1xe2x88x92vP-based semiconductors, so that the GaAs substrate would absorb light emission of 550 nm to 670 nm, which is a wavelength range of (AlxGa1xe2x88x92x)vIn1xe2x88x92vP-based semiconductors. Therefore, out of light emitted from the active layer, the light emitted toward the substrate side would be absorbed within the chip, and could not be extracted outside. Accordingly, for (AlxGa1xe2x88x92x)vIn1xe2x88x92vP-based LEDs, with a view to fabricating a high-efficiency, high-intensity LED, it is important to provide a DBR (distributed Bragg reflector) layer 4 in which low-refractive-index layer and high-refractive-index layer are combined one after another between the GaAs substrate 1 and the active layer 6 as shown in FIG. 11 so as to obtain an enhanced reflectance through multiple reflection. In this example of FIG. 11, (Al0.65Ga0.35)0.5In0.49P (refractive index: 3.51) that does not absorb the emission wavelength 570 nm of the active layer is selected as the high-refractive-index material, and Al0.51In0.49P (refractive index: 3.35) is selected as the low-refractive-index material, while optical film thicknesses of the individual low-refractive-index layer and high-refractive-index layer are set to xcex/4 relative to an emission wavelength of xcex. These materials are stacked alternately to an extent of 10 pairs so as to be enhanced in reflectance, by which the total photoreflection-layer reflectance is set to about 50%. In a case where such an AlGaInP-based light-reflecting layer is provided, reflectance characteristics against the number of pairs are shown in FIG. 13A. The expression xe2x80x9cAlInP/Q(0.4)xe2x80x9d in the figure indicates a characteristic with the use of a pair of (Al0.65Ga0.35)0.51In0.49P and Al0.51In0.49P. Similarly, the expression xe2x80x9cAlInP/Q(0.5)xe2x80x9d indicates a characteristic with the use of a pair of (Al0.55Ga0.45)0.51In0.49P and Al0.51In0.49P. With this light-reflecting layer adopted, the chip luminous intensity can be improved from 20 mcd to 35 mcd, compared with the case where no light-reflecting layer is provided.
As is well known, if the layer thickness of crystals is xe2x80x9cdxe2x80x9d and the refractive index is xe2x80x9cn,xe2x80x9d then the optical film thickness is given by xe2x80x9cnd.xe2x80x9d
As shown in FIG. 12, in (AlxGa1xe2x88x92x)vIn1xe2x88x92vP-based LEDs is used a light-reflecting layer 14 which is formed by stacking a pair of AlxGa1xe2x88x92xAs and AlAs and which has lattice matching with the GaAs substrate. In a case where such an AlGaAs-based light-reflecting layer 14 is provided, reflectance characteristics against the number of pairs are shown in FIG. 13B. In the figure, a broken line expressed as xe2x80x9cAl0.60xe2x80x9d shows a characteristic with the provision of a light-reflecting layer which is formed by selecting Al0.65Ga0.35As (refractive index: 3.66), which does not absorb the emission wavelength 570 nm of the active layer, as the high-refractive-index material and selecting AlAs (refractive index: 3.10) as the low-refractive-index material, and then stacking alternately these materials as a pair. Similarly, a broken line expressed as xe2x80x9cAl0.70xe2x80x9d in the figure shows a characteristic with the use of a pair of Al0.70Ga0.30As and AlAs, and a solid line expressed as xe2x80x9cAl0.75xe2x80x9d in the figure shows a characteristic with the use of a pair of Al0.65Ga0.35As and AlAs. As a result of this, in the case where Al0.65Ga0.35As (refractive index: 3.66) is selected as the high-refractive-index material and AlAs (refractive index: 3.10) is selected as the low-refractive-index material, it becomes possible to provide a larger difference in refractive index than in the case shown in FIG. 13A, where the total reflectance of the light-reflecting layer can be made to be about 60%. With this light-reflecting layer adopted, the chip luminous intensity can be improved from 20 mcd to 40 mcd, compared with the case where no light-reflecting layer is provided.
In this connection, as can be understood from FIGS. 13A and 13B, in order to obtain a high reflectance of 90% or more, which allows the luminous intensity to be improved double or more, the number of semiconductor layer pairs constituting the light-reflecting layer 4, 14 needs to be 30 or more. This is due to very small differences in refractive index, which are 0.18 in the case of (AlxGa1xe2x88x92x)0.51In0.49P(x=0.45)/Al0.51In0.49P and 0.32 or so in the case of AlAs/AlxGa1xe2x88x92xAs.
However, providing a pair number of 30 or more would cause the growth time to be prolonged, which would lead to lower mass-productivity. Also, small differences in refractive index would cause the half-value width of the reflection spectrum to be narrowed, where only a slight change in layer thickness of the light-reflecting layer would cause the reflection spectrum to be largely shifted, making it difficult to obtain a matching between emission wavelength and light-reflecting layer, which would lead to lower reproducibility and so lower mass-productivity. Further, with the number of pairs increased, the light-reflecting layer alone would take a layer thickness as thick as 3 xcexcm or more, where the substrate after epitaxial growth would be liable to warp or deformation, making it difficult to subject the substrate to subsequent processes.
These circumstances are the same also with semiconductor light-emitting devices using other various materials without being limited to the AlGaInP-based materials.
Accordingly, an object of the present invention is to provide a semiconductor light-emitting device capable of effectively extracting light emitted from the active layer to the external.
Another object of the present invention is to provide a semiconductor light-emitting device manufacturing method capable of fabricating such semiconductor light-emitting devices with high mass-productivity.
Still further object of the present invention is to provide an LED lamp and LED display equipped with such semiconductor light-emitting devices.
In order to achieve the above object, the semiconductor light-emitting device of the present invention has the following constitution. That is, the semiconductor light-emitting device of the present invention is formed by stacking, on a semiconductor substrate, a plurality of layers including an active layer made of a semiconductor which generates light of a specified wavelength. Furthermore, the semiconductor light-emitting device comprises a first light-reflecting layer provided between the semiconductor substrate and the active layer and having a main reflecting part including a dielectric containing Al or space and a sub reflecting part made of a semiconductor layer containing Al.
In the semiconductor light-emitting device of this invention, between the semiconductor substrate and the active layer is a first light-reflecting layer having a main reflecting part including a dielectric containing Al or space and a sub reflecting part made of a semiconductor layer containing Al. The main reflecting part of this first light-reflecting layer, by virtue of its including an dielectric containing Al or space, becomes lower in refractive index xe2x80x9cnxe2x80x9d than the sub reflecting part formed of a semiconductor layer containing Al. Accordingly, light emitted by the active layer is reflected at a high reflectance by the main reflecting part of the first light-reflecting layer. If the main reflecting part of the first light-reflecting layer is disposed at a necessary region, e.g., at a region where the electrode is absent on the active layer, then the light emitted by the active layer is reflected by the main reflecting part of the first light-reflecting layer so as to go outside without being interrupted by the electrode. Therefore, light emitted from the active layer can be extracted outside effectively.
In one embodiment, the semiconductor light-emitting device further comprises a second light-reflecting layer provided between the first light-reflecting layer and the active layer and formed by stacking a plurality of pairs of a low-refractive-index material layer and a high-refractive-index material layer.
In the semiconductor light-emitting device of this one embodiment, between the first light-reflecting layer and the active layer is a second light-reflecting layer formed by stacking a plurality of pairs of a low-refractive-index material layer and a high-refractive-index material layer. Therefore, light emitted from the active layer can be extracted outside further effectively. Also, by virtue of a low refractive index xe2x80x9cnxe2x80x9d of the main reflecting part of the first light-reflecting layer, a high reflectance can be obtained even with a small number of pairs of the second light-reflecting layer.
Desirably, the second light-reflecting layer is a distributed Bragg reflector (DBR).
In one embodiment of the semiconductor light-emitting device, the semiconductor substrate is of a first conductive type, and a second-conductive-type current spreading layer is provided on the active layer. The semiconductor light-emitting device further comprises a first-conductive-type current blocking layer provided at a specified region inside the current spreading layer, and an electrode layer provided on an top surface of the current spreading layer and at a region corresponding to the current blocking layer. Furthermore, the sub reflecting part of the first light-reflecting layer is disposed at a region corresponding to the current blocking layer, and the main reflecting part of the first light-reflecting layer is disposed at a region corresponding to surroundings of the current blocking layer.
In the semiconductor light-emitting device of this one embodiment, electric current injected from the electrode layer into the current spreading layer is interrupted by the current blocking layer provided at a specified region inside the current spreading layer, and thus flows in more part to the surrounding region of the current blocking layer. As a result, light emission occurs more in a portion of the active layer corresponding to the surroundings of the current blocking layer. Since the main reflecting part of the first light-reflecting layer is disposed at a region corresponding to the surroundings of the current blocking layer, light emitted at the portion of the active layer corresponding to the surroundings of the current blocking layer is reflected by the main reflecting part of the first light-reflecting layer so as to go outside without being interrupted by the electrode. Therefore, light emitted from the active layer can be extracted outside effectively.
In one embodiment of the semiconductor light-emitting device, the sub reflecting part of the first light-reflecting layer is formed of any one kind of semiconductor selected from among AlxGa1xe2x88x92xAs, (AlxGa1xe2x88x92x)vIn1xe2x88x92vP, (AlxGa1xe2x88x92x)vIn1xe2x88x92vN, (AlxGa1xe2x88x92x)vIn1xe2x88x92vAs, and (AlxGa1xe2x88x92x)vIn1xe2x88x92vSb (where 0 less than xxe2x89xa61 and 0 less than v less than 1), and the main reflecting part of the first light-reflecting layer is formed of AlOy (where y is a positive real number) or space.
Herein, aluminium oxide is expressed uniformly as AlOy, and AlOy is synonymous with AlxOy (where x and y are positive real numbers).
In addition, it is assumed that suffixes xe2x80x9cx,xe2x80x9d xe2x80x9cvxe2x80x9d xe2x80x9cyxe2x80x9d and the like representing compositions can take independent values between and among different compounds.
In one embodiment of the semiconductor light-emitting device, the sub reflecting part of the first light-reflecting layer is formed of any one kind of multilayer film selected from among a multilayer film in which AlxGa1xe2x88x92xAs layer and AlzGa1xe2x88x92zAs layer are alternately stacked, a multilayer film in which (AlxGa1xe2x88x92x)vIn1xe2x88x92vP layer and (AlzGa1xe2x88x92z)vIn1xe2x88x92vP layer, alternately stacked, a multilayer film in which (AlxGa1xe2x88x92x)vIn1xe2x88x92vN layer and (AlzGa1xe2x88x92z)vIn1xe2x88x92vN layer alternately stacked, a multilayer film in which (AlxGa1xe2x88x92x)vIn1xe2x88x92vAs layer and (AlzGa1xe2x88x92z)vIn1xe2x88x92vAs layer are alternately stacked, and a multilayer film in which (AlxGa1xe2x88x92x)vIn1xe2x88x92vSb layer and (AlzGa1xe2x88x92z)vIn1xe2x88x92vSb layer are alternately stacked (where 0 less than x less than zxe2x89xa61 and 0 less than v less than 1), and the main reflecting part of the first light-reflecting layer is formed of a multilayer film in which any one kind of semiconductor selected from among AlxGa1xe2x88x92xAs, (AlxGa1xe2x88x92x)vIn1xe2x88x92vP, (AlxGa1xe2x88x92x)vIn1xe2x88x92vN, (AlxGa1xe2x88x92x)vIn1xe2x88x92vAs, and (AlxGa1xe2x88x92x)vIn1xe2x88x92vSb (where 0 less than xxe2x89xa61 and 0 less than v less than 1) in correspondence to the multilayer film forming the sub reflecting part, and AlOy layer (where y is a positive real number) or a space layer, are alternately stacked.
As described in conjunction with the prior art, in order to enhance the light extraction efficiency by obtaining a high reflectance with the light-reflecting layer so that higher brightness and higher output can be achieved, given that the light-reflecting layer is a single layer, there is a need for obtaining a larger difference in refractive index between two layers that define the reflecting surface of the light-reflecting layer. Also, when the light-reflecting layer is formed of a multilayer film, it is necessary to obtain a larger difference in refractive index between a pair of semiconductor films constituting the light-reflecting layer. However, for is example, in the case of (AlxGa1xe2x88x92x)vIn1xe2x88x92vP-based LEDs, materials that are free from light absorption and that come into lattice matching with the active layer are limited to (AlxGa1xe2x88x92x)vIn1xe2x88x92vP-based materials or AlxGa1xe2x88x92xAs-based materials, which are compound semiconductor materials in either case, where the refractive index can be changed only within a range of 2.9 to 3.5 or so at most.
On the other hand, a principle diagram of the reflection layer of the present invention is shown in FIG. 1. This is a structure in which on a semiconductor substrate xe2x80x9caxe2x80x9d are deposited, in this order, an AlOy oxide layer xe2x80x9cb,xe2x80x9d which is formed by oxidizing AlAs, an AlxGa1xe2x88x92xAs layer, a light-reflecting layer xe2x80x9cc,xe2x80x9d which is formed by alternately stacking a high-refractive-index semiconductor material and a low-refractive-index semiconductor material, and an active layer xe2x80x9cd.xe2x80x9d In contrast to this, the prior art includes no AlOy oxide layer xe2x80x9cb.xe2x80x9d With the shown arrangement, there can be provided a refractive index difference as large as 0.6 to 1.4 or so between the light-reflecting layer xe2x80x9ccxe2x80x9d and the AlOy layer xe2x80x9cb.xe2x80x9d Therefore, the reflectance at the interface between the light-reflecting layer xe2x80x9ccxe2x80x9d and the AlOy layer xe2x80x9cbxe2x80x9d becomes larger, so that a larger reflectance can be obtained as compared with normal light-reflecting layers. For example, as shown in FIG. 2, according to the present invention, a higher reflectance can be obtained as compared with the case where the AlOy layer is not provided (prior art), and yet the half-value width of the reflection spectrum can be increased (the wavelength range with high reflectance is widened).
Meanwhile, a principle diagram of another reflection layer according to the present invention is shown in FIG. 3. This is a structure in which on a semiconductor substrate xe2x80x9caxe2x80x9d are deposited, in this order, a light-reflecting layer xe2x80x9cf,xe2x80x9d which is formed by alternately stacking AlAs layer and AlxGa1xe2x88x92xAs layer and further changing the AlAs layer into an AlOy layer (where y is a positive real number) xe2x80x9cb,xe2x80x9d and an active layer xe2x80x9cd.xe2x80x9d As compared with the conventional light-reflecting layer in which AlAs layer and AlxGa1xe2x88x92xAs layer are alternately stacked as they are, in contrast to this, there can be provided a refractive index difference as large as 0.6 to 1.4 or so between the AlOy layer and the AlxGa1xe2x88x92xAs layer. As a result, reflection characteristic of the light-reflecting layer xe2x80x9cfxe2x80x9d shows a high reflectance of 99% at maximum as shown in FIG. 4, with its wavelength range also widened. Further, since the reflectance abruptly decreases for light of wavelengths falling outside the necessary wavelength range, the semiconductor light-emitting device is enhanced in color purity as another advantage. As in the case of FIG. 1, even with variations or fluctuations in layer thickness, reflectance and reflection spectrum are less liable to variations, hence a high mass productivity.
Al is strong in bond with oxygen, so highly oxidation-prone, and only by leaving it in the air, Al oxide is formed. However, the Al oxide film formed only by natural oxidation as shown above is poor in characteristics, exemplified by large numbers of voids in the film. Accordingly, for example, leaving an AlxGa1xe2x88x92xAs layer (in particular, one having an Al composition of nearly 1) in a water vapor atmosphere at a temperature of 300xc2x0 C. to 400xc2x0 C. allows Al to be oxidized by high-temperature water vapor, so that stabler AlOy layer can be formed (e.g., Specification of U.S. Pat. No. 5,517,039, or Kenichi Iga et al., xe2x80x9cFundamentals and Applications of Plane Emission Laser,xe2x80x9d Kyoritsu Shuppan K. K., June 1999, pp. 105-113.) This AlOy layer, because of being an oxide (dielectric), is much lower in refractive index xe2x80x9cnxe2x80x9d than semiconductor materials, taking a value of n=2.5 to 1.9. Accordingly, by changing the AlxGa1xe2x88x92xAs layer into an AlOy layer so that the refractive index is lowered, the reflectance for the light emitted by the active layer can be enhanced. Thus, a high reflectance can be obtained even with a small number of pairs in the light-reflecting layer, and the light emitted from the active layer can be extracted outside effectively.
Also, the AlOy layer, because of being an oxide (dielectric), is large in band gap, and transparent to blue to red visible light regions. Therefore, according to the present invention, a high-quality light-reflecting layer which is very small in wavelength dependence and which is close to 100% in reflectance can be formed. As a result of this, it is no longer necessary to laboriously select an Al composition which is free from absorption to emission wavelength, as would be involved in the light-reflecting layer made of semiconductor materials of the prior art.
According to the present invention, a high reflectance can be obtained as compared with the case where the AlOy layer is not provided (prior art), and yet the half-value width of the reflection spectrum can be increased. As a result, even with variations or fluctuations in layer thickness of the light-reflecting layer, reflectance and reflection spectrum are less liable to variations, hence a high mass productivity.
Since the low-refractive-index Al rich layer xe2x80x9cf2xe2x80x9d constituting the light-reflecting layer becomes an AlOy layer having an even lower refractive index, the reflectance for the light emitted by the active layer can be enhanced. Thus, a high reflectance can be obtained even with a small number of pairs of the light-reflecting layer, and the light emitted from the active layer can be extracted outside effectively. For example, as shown in FIG. 4, according to the present invention, a higher reflectance can be obtained as compared with the case where the AlOy layer is not changed into an AlOy layer (prior art), and yet the half-value width of the reflection spectrum can be increased. As a result, even with variations or fluctuations in layer thickness of the light-reflecting layer, reflectance and reflection spectrum are less liable to variations, hence a high mass productivity.
FIG. 5 shows a pair-number dependence of the reflectance of the light-reflecting layer according to the present invention, in comparison with prior arts. In the figure, a solid line xcex1 connecting marks xe2x80x9cxe2x80xa2xe2x80x9d to one another shows a characteristic with the use of a pair of a low-refractive-index AlOy layer and a high-refractive-index Al0.60Ga0.40As layer according to the present invention, while the other lines xcex21, xcex22, xcex23, xcex24 and xcex25 show characteristics with the use of known pairs. More specifically, xcex21 shows a characteristic with the use of a pair of Al0.75Ga0.25As layer and AlAs layer, xcex22 shows a characteristic with the use of a pair of Al0.70Ga0.30As layer and AlAs layer, xcex23 shows a characteristic with the use of a pair of Al0.60Ga0.40As layer and AlAs layer, xcex24 shows a characteristic with the use of a pair of (Al0.40Ga0.60)0.51In0.49P layer and Al0.51In0.49P layer, and xcex25 shows a characteristic with the use of a pair of (Al0.50Ga0.50)0.51In0.49P layer and Al0.51In0.49P layer. As can be understood from the figure, according to the present invention, the light-reflecting layer, by virtue of its large refractive index difference, can achieve a reflectance of almost 100% even with a few pairs of the light-reflecting layer. Thus, the growth time can be reduced and a high mass productivity can be obtained.
The method for manufacturing a semiconductor light-emitting device of the present invention has the following constitution. That is, the method for manufacturing a semiconductor light-emitting device of the present invention is one of stacking, on a semiconductor substrate, a plurality of layers including an active layer made of a semiconductor which generates light of a specified wavelength. Furthermore, the method comprising the steps of:
providing, between the semiconductor substrate and the active layer, an Al rich layer higher in Al ratio than any other layer among the plurality of layers;
dividing into chips a wafer in which the plurality of layers are stacked, thereby making a side face of the Al rich layer exposed; and
oxidizing Al contained in the Al rich layer from the exposed side face, thereby making a peripheral portion of the Al rich layer changed into an AlOy layer.
In the semiconductor light-emitting device manufacturing method of this invention, peripheral portion of the Al rich layer is changed into an AlOy layer (dielectric) so that the refractive index is lowered, by which the reflectance for the light emitted by the active layer can be enhanced. Thus, the light emitted from the active layer can be extracted outside effectively.
In one embodiment of the method for manufacturing a semiconductor light-emitting device, the step of oxidizing Al contained in the Al rich layer is carried out by leaving in a water vapor the chips in which the side face of the Al rich layer is exposed.
In one embodiment of the method for manufacturing a semiconductor light-emitting device, the water vapor is introduced to the side face of the Al rich layer by an inert gas that has been passed through boiling water.
In one embodiment of the method for manufacturing a semiconductor light-emitting device, the step of oxidizing Al contained in the Al rich layer is carried out in an atmosphere having a temperature of 300xc2x0 C. to 400xc2x0 C.
In one embodiment, the method for manufacturing a semiconductor light-emitting device further comprises the step of removing, by etching, the AlOy layer formed at the peripheral portion of the Al rich layer.
In the semiconductor light-emitting device manufacturing method of this one embodiment, since the space region formed by the removal of the AlOy layer has a refractive index of 1, a nearly total reflection state can be obtained at the chip peripheral portion of the rear side of the active layer. Thus, the light emitted from the active layer can be extracted outside effectively.
Also, according to the present invention, there is provided an LED lamp which comprises the semiconductor light-emitting device as defined above.
In one embodiment of the LED lamp, as said semiconductor light-emitting device, a plurality of semiconductor light-emitting devices having different wavelengths from each other are integrally provided, and the semiconductor light-emitting devices are connected in the manner that they can be applied with electric current independently from each other.
Also, according to the present invention, there is provided an LED display in which the LED lamp as defined above is arrayed in a matrix.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, including the step of forming an electrode for electrical conduction at a region above the active layer corresponding to a remaining portion of the Al rich layer that is not changed into the AlOy layer.
In the semiconductor light-emitting device manufacturing method of this one embodiment, an electrode is formed at a region above the active layer corresponding to a remaining portion of the Al rich layer that is not changed into the AlOy layer. Therefore, out of the Al rich layer, the region corresponding to the portion that has been changed into the AlOy layer can be prevented from being occupied by the electrode. Thus, the light generated by the active layer and reflected by the AlOy layer can be extracted outside effectively without being interrupted by the electrode.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, including the step of forming a current blocking layer for blocking electric current at a region corresponding to a remaining portion of the Al rich layer that is not changed into the AlOy layer.
In the semiconductor light-emitting device manufacturing method of this one embodiment, a current blocking layer for blocking electric current is formed at a region corresponding to its remaining portion that is not changed into the AlOy layer. Therefore, a larger amount of electric current flows through the region corresponding to the AlOy layer, as compared with the case where the current blocking layer is not formed. Thus, the light generated by the active layer and reflected by the AlOy layer can be extracted outside effectively.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, wherein the light-reflecting layer is formed by alternately stacking a layer containing Al and having a specified Al composition and an AlOy layer, and thickness of one layer which is among the layers forming the light-reflecting layer and which is adjacent to the layer containing Al and changed into the AlOy layer is set to a quarter of the wavelength.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, further including the step of, after dividing the layers into chips, making the Al rich layer changed into the AlOy layer from its exposed end face, where a remaining portion of the Al rich layer that is not changed into the AlOy layer is made coincident in configuration with the electrode above the active layer.
In the semiconductor light-emitting device manufacturing method of this one embodiment, it is no longer necessary to laboriously select an Al composition which is free from absorption to emission wavelength, as would be involved in the light-reflecting layer made of semiconductor materials of the prior art.
In another aspect of the semiconductor light-emitting device of this invention, there is provided a semiconductor light-emitting device having on a semiconductor substrate a light-emitting layer which generates light of a specified wavelength, the semiconductor light-emitting device further including, between the semiconductor substrate and the light-emitting layer, a semiconductor layer which has a refractive index varying with respect to a layer direction so as to reflect light emitted by the light-emitting layer.
It is noted here that the terms, xe2x80x9clayer direction,xe2x80x9d refer to a direction extending along the layer, i.e., a direction (planar direction) along which the layer spreads.
In the semiconductor light-emitting device of this invention, between the semiconductor substrate and the light-emitting layer, is provided a semiconductor layer which has a refractive index varying with respect to a layer direction so as to reflect light emitted by the light-emitting layer. The refractive index of this semiconductor layer is so set as to be lower in a necessary region, for example, a region where the electrode is absent above the light-emitting layer, by which the reflectance for the light emitted by the light-emitting layer can be enhanced. Thus, a high reflectance can be obtained even with a small number of pairs in the light-reflecting layer, and the light emitted from the light-emitting layer can be extracted outside effectively.
As already described, in order to enhance the light extraction efficiency by obtaining a high reflectance with the light-reflecting layer so that higher brightness and higher output can be achieved, there is a need for obtaining a larger difference in refractive index between a pair of semiconductor films constituting the light-reflecting layer. However, for example, in the case of (AlxGa1xe2x88x92x)vIn1xe2x88x92vP-based LEDs, materials that are free from light absorption and that come into lattice matching with the light-emitting layer are limited to (AlxGa1xe2x88x92x)vIn1xe2x88x92vP-based materials or AlxGa1xe2x88x92xAs-based materials, which are compound semiconductor materials in either case, where the refractive index can be changed only within a range of 2.9 to 3.5 or so at most.
Accordingly, as a method for manufacturing a semiconductor light-emitting device in the present invention, there is provided a semiconductor light-emitting device manufacturing method including a step of providing on a semiconductor substrate a light-emitting layer which generates light of a specified wavelength, the method further comprising the steps of depositing an AlxGa1xe2x88x92xAs layer and the light-emitting layer on the semiconductor substrate in this order, and making part of the AlxGa1xe2x88x92xAs layer in the layer direction changed into an AlOy layer (where y is a positive real number).
Al in the AlxGa1xe2x88x92xAs layer is strong in bond with oxygen, so highly oxidation-prone, and when it is left in the air, Al oxide is formed. Accordingly, oxidizing an AlxGa1xe2x88x92xAs layer (in particular, one having an Al composition xe2x80x9cxxe2x80x9d of nearly 1) in a water vapor at a temperature of 300xc2x0 C. to 400xc2x0 C. allows a stable AlOy layer to be formed. This AlOy layer, because of being an oxide containing Al, is much lower in refractive index xe2x80x9cnxe2x80x9d than semiconductor materials, taking a value of n=2.5 to 1.9. Accordingly, by changing the AlxGa1xe2x88x92xAs layer into an AlOy layer so that the refractive index is lowered, the reflectance for the light emitted by the light-emitting layer can be enhanced. Thus, a high reflectance can be obtained even with a small number of pairs in the light-reflecting layer, and the light emitted from the light-emitting layer can be extracted outside effectively.
Also, the AlOy layer, because of being an oxide, is large in band gap, and transparent to visible light regions, particularly a region of 560 nm to 650 nm, which is the emission region of (AlxGa1xe2x88x92x)vIn1xe2x88x92vP-based materials. Therefore, according to the present invention, a high-quality light-reflecting layer which is very small in wavelength dependence and which is close to 100% in reflectance can be formed. As a result of this, it is no longer necessary to laboriously select an Al composition which is free from absorption to emission wavelength, as would be involved in the light-reflecting layer made of semiconductor materials of the prior art.
In a method for manufacturing a semiconductor light-emitting device in one embodiment, as illustrated in FIG. 1, an AlxGa1xe2x88x92xAs layer, a light-reflecting layer xe2x80x9ccxe2x80x9d in which a high-refractive-index material and a low-refractive-index material are alternately stacked, and a light-emitting layer xe2x80x9cdxe2x80x9d are deposited in this order on a semiconductor substrate xe2x80x9ca,xe2x80x9d and then part of the AlxGa1xe2x88x92xAs layer in the layer direction is changed into an AlOy layer xe2x80x9cbxe2x80x9d (FIG. 1, however, shows only a region that has been changed into the AlOy layer). With such an arrangement, a refractive index difference as large as 0.6 to 1.4 or so can be provided between the light-reflecting layer xe2x80x9ccxe2x80x9d and the AlOy layer xe2x80x9cb.xe2x80x9d Therefore, the reflectance at the interface between the light-reflecting layer xe2x80x9ccxe2x80x9d and the AlOy layer xe2x80x9cbxe2x80x9d becomes larger, so that a larger reflectance can be obtained as compared with normal light-reflecting layers. For example, as shown in FIG. 2, according to the present invention, a higher reflectance can be obtained as compared with the case where the AlOy layer is not provided (prior art), and yet the half-value width of the reflection spectrum can be increased. As a result, even with variations or fluctuations in layer thickness of the light-reflecting layer, reflectance and reflection spectrum are less liable to variations, hence a high mass productivity.
In a method for manufacturing a semiconductor light-emitting device in one embodiment, as illustrated in FIG. 3, a light-reflecting layer xe2x80x9cfxe2x80x9d in which a high-refractive-index semiconductor material xe2x80x9cf1xe2x80x9d and a low-refractive-index AlxGa1xe2x88x92xAs layer xe2x80x9cf2xe2x80x9d (where 0 less than xxe2x89xa61) are alternately stacked, and a light-emitting layer xe2x80x9cdxe2x80x9d are deposited in this order on a semiconductor substrate xe2x80x9ca,xe2x80x9d and then part of the AlxGa1xe2x88x92xAs layer xe2x80x9cf2xe2x80x9d in the layer direction is changed into an AlOy layer (FIG. 3, however, shows only a region (dotted) that has been changed into the AlOy layer). With such an arrangement, the low-refractive-index AlxGa1xe2x88x92xAs layer xe2x80x9cf2xe2x80x9d constituting the light-reflecting layer becomes an AlOy layer having an even lower refractive index, so that the reflectance for the light emitted by the light-emitting layer can be enhanced. Thus, a high reflectance can be obtained even with a small number of pairs in the light-reflecting layer, and the light emitted from the light-emitting layer can be extracted outside effectively. For example, as shown in FIG. 4, according to the present invention, a higher reflectance can be obtained as compared with the case where the AlxGa1xe2x88x92xAs layer is not changed into the AlOy layer (prior art), and yet the half-value width of the reflection spectrum can be increased. As a result, even with variations or fluctuations in layer thickness of the light-reflecting layer, reflectance and reflection spectrum are less liable to variations, hence a high mass productivity.
FIG. 5 shows a pair-number dependence of the reflectance of the light-reflecting layer according to the present invention, in comparison with prior arts. According to the present invention, the light-reflecting layer, by virtue of its large refractive index difference, can achieve a reflectance of almost 100% even with a few pairs of the light-reflecting layer. Thus, the growth time can be reduced and a high mass productivity can be obtained.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, including the steps of making part of the AlxGa1xe2x88x92xAs layer in the layer direction changed into an AlOy layer, and thereafter removing the AlOy layer.
In the semiconductor light-emitting device manufacturing method of this one embodiment, since the space region formed by the removal of the AlOy layer has a refractive index of 1, a nearly total reflection state can be obtained at the chip peripheral portion on the rear side of the light-emitting layer. Thus, the light emitted from the light-emitting layer can be extracted outside effectively.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, including the step of forming an electrode for electrical conduction at a region above the light-emitting layer corresponding to a remaining portion of the AlxGa1xe2x88x92xAs layer that is not changed into the AlOy layer.
In the semiconductor light-emitting device manufacturing method of this one embodiment, an electrode is formed at a region above the light-emitting layer corresponding to a remaining portion of the AlxGa1xe2x88x92xAs layer that is not changed into the AlOy layer. Therefore, out of the AlxGa1xe2x88x92xAs layer, the region corresponding to the portion that has been changed into the AlOy layer can be prevented from being occupied by the electrode. Thus, the light generated by the light-emitting layer and reflected by the AlOy layer can be extracted outside effectively without being interrupted by the electrode.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, comprising the steps of forming a current blocking layer for blocking electric current at a region above the light-emitting layer corresponding to a remaining portion of the AlxGa1xe2x88x92xAs layer that is not changed into the AlOy layer.
In the semiconductor light-emitting device manufacturing method of this one embodiment, a current blocking layer for blocking electric current is formed at a region above the light-emitting layer corresponding to a remaining portion of the AlxGa1xe2x88x92xAs layer that is not changed into the AlOy layer. Therefore, a larger amount of electric current flows through the region corresponding to the AlOy layer, as compared with the case where the current blocking layer is not formed. Thus, the light generated by the light-emitting layer and reflected by the AlOy layer can be extracted outside effectively.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, including the steps of forming the light-reflecting layer by alternately stacking an AlxGa1xe2x88x92xAs layer having a specified Al composition (where 0 less than xxe2x89xa61) and an AlOy layer, wherein thickness of one layer which is among the AlxGa1xe2x88x92xAs layers forming the light-reflecting layer and which is adjacent to the AlxGa1xe2x88x92xAs layer changed into the AlOy layer is set to a quarter of the wavelength.
In the semiconductor light-emitting device manufacturing method of this one embodiment, the reflectance for the light emitted by the light-emitting layer is further enhanced at the region corresponding to the AlOy layer.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, including the step of forming the light-emitting layer from an (AlxGa1xe2x88x92x)vIn1xe2x88x92vP-based material.
In the semiconductor light-emitting device manufacturing method of this one embodiment, a semiconductor light-emitting device having an emission wavelength band of 560 nm to 650 nm, is fabricated.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, further including the step of, after dividing the layers into chips, making the AlxGa1xe2x88x92xAs layer changed into the AlOy layer from its exposed end face, where a remaining portion of the AlxGa1xe2x88x92xAs layer that is not changed into the AlOy layer is made coincident in configuration with the electrode above the light-emitting layer.
In the semiconductor light-emitting device manufacturing method of this one embodiment, since the AlxGa1xe2x88x92xAs layer is changed into the AlOy layer from its exposed end face, the AlOy layer can be formed stably and easily, hence a high mass productivity. Still, since the remaining portion of the AlxGa1xe2x88x92xAs layer that is not changed into the AlOy layer is made coincident in configuration with the electrode on the light-emitting layer, the region out of the AlxGa1xe2x88x92xAs layer corresponding to the portion that has been changed into the AlOy layer can be prevented from being occupied by the electrode. Thus, the light generated by the light-emitting layer and reflected by the AlOy layer can be extracted outside effectively without being interrupted by the electrode.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, further including the step of, after dividing the layers into chips, making the AlxGa1xe2x88x92xAs layer changed into the AlOy layer from its exposed end face, where a remaining portion of the AlxGa1xe2x88x92xAs layer that is not changed into the AlOy layer is made coincident in configuration with the current blocking layer.
In the semiconductor light-emitting device manufacturing method of this one embodiment, since the AlxGa1xe2x88x92xAs layer is changed into the AlOy layer from its exposed end face, the AlOy layer can be formed stably and easily, hence a high mass productivity. Still, since the remaining portion of the AlxGa1xe2x88x92xAs layer that is not changed into the AlOy layer is made coincident in configuration with the current blocking layer, a large amount of electric current flows through the region corresponding to the AlOy layer. Thus, the light generated by the light-emitting layer and rfeflected by the AlOy layer can be extracted outside effectively.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, wherein an AlxGa1xe2x88x92xP layer, an AlxIn1xe2x88x92xP layer or an AlxIn1xe2x88x92xAs layer is used in place of the AlxGa1xe2x88x92xAs layer.
Also, as a method for manufacturing a semiconductor light-emitting device according to the present invention, there is provided a semiconductor light-emitting device manufacturing method including the step of providing above a semiconductor substrate a light-emitting layer which generates light of a specified wavelength. The method further includes the steps of: depositing on the semiconductor substrate, in an order given below, a light-reflecting layer in which an AlxGa1xe2x88x92xAs layer (where 0 less than xxe2x89xa61) having a specified Al composition and an (AlxGa1xe2x88x92x)vIn1xe2x88x92vP layer (where 0 less than xxe2x89xa61 and 0 less than v less than 1) are alternately stacked and which serves for reflecting the light of the wavelength, and the light-emitting layer; and making part of the AlxGa1xe2x88x92xAs layer in the layer direction changed into an AlOy layer (where y is a positive real number).
In the semiconductor light-emitting device manufacturing method of this invention, by changing the AlxGa1xe2x88x92xAs layer into an AlOy layer so that the refractive index is lowered, the reflectance for the light emitted by the light-emitting layer can be enhanced. Thus, a high reflectance can be obtained even with a small number of pairs in the light-reflecting layer, and the light emitted from the light-emitting layer can be extracted outside effectively.
Also, the AlOy layer, because of being an oxide, is large in band gap, and transparent to visible light regions, particularly a region of 560 nm to 670 nm, which is the emission region of (AlxGa1xe2x88x92x)vIn1xe2x88x92vP-based materials. Therefore, according to the present invention, a high-quality light-reflecting layer which is very small in wavelength dependence and which is close to 100% in reflectance can be formed. As a result of this, it is no longer necessary to laboriously select an Al composition which is free from absorption to emission wavelength, as would be involved in the light-reflecting layer made of semiconductor materials of the prior art.
In one embodiment, there is provided a method for manufacturing a semiconductor light-emitting device, further including the step of, after the step of making part of the AlxGa1xe2x88x92xAs layer in the layer direction changed into an AlOy layer, removing the AlOy layer by using a hydrofluoric acid-based etching solution.
In the semiconductor light-emitting device manufacturing method of this one embodiment, only the AlOy layer can be selectively etched and thereby removed out of AlxGa1xe2x88x92xAs layer or the like.